Urban Estuarine Beaches and Urban Water Cycle Seepage: The Influence of Temporal Scales

Abstract

Abstract:Temperate estuarine beaches are an asset to coastal cities. Being located within the transition zone where the river meets the sea can provide several environmental benefits such as warm water temperature during the summer, flat waters, protection from coastal upwelling-induced morning fog, as well as additional recreational and cultural values. In this study we address a major question-can the urban water cycle impair the water quality dynamics during a bathing season in a temperate Atlantic estuary (Douro, Northwest Portugal)? Water quality was assessed according to the EU legal criteria at different time scales. No daily, weekly, or monthly patterns for microbiological descriptors were found, which rather followed the hourly tidal dynamics. Quality decreased during high tide, affecting potentially 800+ beach-users during mid-summer weekends (4 m 2 per person). Low water quality was transported upstream from highly populated urban areas. Therefore, the understanding of the dynamics of estuarine systems is essential to adapt the standard official approach, and the obtained results can be used to draw policy recommendations to improve the sampling strategy, aiming for more accurate assessment of the water quality to reduce the risk hazard of estuarine beaches.

A importância dos modelos numéricos na previsão dos efeitos das alterações climáticas e dos eventos extremos em áreas estuarinas

“…O estuário do Douro é considerado como sendo um ecossistema com alto impacto antropogénico, localizado numa área altamente urbanizada, com instalações portuárias, atividades e estruturas comerciais, pesqueiras e turísticas, efluentes industriais e urbanos, e descarga de efluentes agrícolas e de esgotos domésticos, onde numerosos contaminantes têm sido encontrados (Almeida et al, 2006;Costa-Dias et al, 2018;Gouveia et al, 2018;Gravato et al, 2010;Guimarães et al, 2009;Iglesias et al, 2020;Mucha et al, 2004). Para caudais superiores a 700 m 3 /s, toda a água doce é descarregada no mar, o estuário é preenchido com água doce e a intrusão de água salgada não acontece, mesmo com condições de maré de elevada amplitude.…”